[Intel-gfx] [PATCH 18/24] drm/i915: program iCLKIP on Lynx Point

[Jesse Barnes]

On Thu, 26 Apr 2012 15:21:13 -0300
Eugeni Dodonov <eugeni.dodonov at intel.com> wrote:

> The iCLKIP clock is used to drive the VGA pixel clock on the PCH. In order
> to do so, it must be programmed to properly do the clock ticks according
> to the divisor, phase direction, phase increments and a special auxiliary
> divisor for 20MHz clock.
> 
> Those values can be programmed individually, by doing some math; or we
> could use a pre-defined table of values for each modeset. For speed and
> simplification, the idea was to just adopt the table of valid pixel clocks
> and select the matching iCLKIP values from there.
> 
> As a possible idea for the future, it would be possible to add a fallback
> and calculate those values manually in case no match is found. But I don't
> think we'll encounter a mode not covered by those table, and VGA is pretty
> much going away in the future anyway.
> 
> Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
> ---

I don't mind the table and like the fact that it documents the PPM.
But I think we should fuzzy match the clocks, since e.g. 1920x1080 at 60Hz
with reduced blanking is a 138.5MHz clock, and we don't have a match
for that it appears?  Or do we already fuzzy match elsewhere?

-- 
Jesse Barnes, Intel Open Source Technology Center